The present invention relates to a vinyl chloride resin composition, and more particularly to a vinyl chloride resin composition having an improved impact resistance with an excellent transparency that the vinyl chloride resin itself possesses originally.
A so-called MBS resin wherein methyl methacrylate, styrene and the like are graft-polymerized onto a butadiene rubber has been used as a reinforcing agent for improving the impact resistance of vinyl chloride resins. It is important that the transparency of the resins is not impaired by the incorporation of the reinforcing agent. Various improvements of the reinforcing agent for vinyl chloride resins or of the process for improving the impact resistance of vinyl chloride resins without impairing the transparency of the resins are also proposed, for instance, as disclosed in Japanese Patent Publication Kokai No. 59-221317. However, demand for improvement of the quality of vinyl chloride resin products is still strong and a further improvement is desired.
As a means for markedly increasing the impact resistance imparting ability of the MBS reinforcing agent for vinyl chloride resins, it is well known to increase the butadiene content of the reinforcing agent. For this purpose, it has been attempted to increase the proportion of the rubber component in the reinforcing agent or to increase the butadiene content in the rubber component. However, the former means, namely the increase of the proportion of the rubber, causes a serious problem that since the graft copolymer changes into a massive material during the preparation thereof when the proportion of the rubber component exceeds about 65% by weight, no satisfactory polymer powder is obtained and moreover the incorporation of the produced graft copolymer into vinyl chloride resins lowers the transparency of molded end products. The latter means, namely the increase of the butadiene content in the rubber component, also causes a serious problem that the transparency of molded end products is markedly lowered. Owing to such problems, there has not been provided a reinforcing agent having a butadiene content of not less than 60% by weight which can impart a high impact resistance to vinyl chloride resins without impairing the high transparency of the resins.